Weird question, but why were those engines running rediculously low compression ratios? 5.5:1? Right now we're 8.5:1 on a N/A engine, 7.5:1 on a turbo. Was it the metals?
Compared to the Allison V1710, the AM-38F was a bus engine. Nothing approaching the sophistication of the Allison. Its displacement was huge at 2,847 cubic inches and its max rpm was 2,350 compared to the Allison's 3,000 RPM. It weighed 500 lb more than an Allison of comparable power. Compression was 6.0:1, with the Allison at 6.5:1. Soviet refined avgas was generally poor compared to western fuel, so low compression was lower.
This was a big, slow turning motor that proved to be extremely robust, which was a primary consideration.
My regards,
Widewing
